1. Field of the Invention
Aspects of the present invention relate to an optical disk, and more particularly, to a hybrid disk including first and second recording layers that are different in format from each other.
2. Description of the Related Art
Generally, optical disks are manufactured by employing one of a variety of formats such as a compact disk (CD) format, a digital versatile disk (DVD) format, a high density digital versatile disk (HD-DVD) format, and a blu-ray disk (BD) format.
Recently, a hybrid disk having recording layers that are different in format from each other has been proposed. Wavelengths of beams for writing and reading data on or from the respective recording layers are different from each other. For example, a recording layer having the CD format and a recording layer having the DVD format, or a recording layer having the DVD format and a recording layer having the BD format, or a layer having the CD format and a layer having the BD format can be formed on a single optical disk.
Since the hybrid disk includes recording layers different in format from each other, the data written on the hybrid optical disk can be read by both an existing player and a new player. For example, when the hybrid disk includes recording layers respectively having CD and DVD formats, the hybrid disk can be used in a CD player or a DVD player.
In the hybrid disk, focus servo control is performed using a focus error signal (FES) detected by irradiating a beam having a wavelength proper for each recording layer and using the amplitude of a radio frequency signal (RFS).
However, when the focus servo control is performed by irradiating a beam having a predetermined wavelength to one of the recording layers of the hybrid disk, crosstalk may be generated since a beam reflected from another of the recording layers has a predetermined intensity. That is, in an S-curve, in addition to a signal component reflected from one of the recording layers, a beam having a predetermined intensity or more is reflected from another layer and detected to disturb the focus servo control. For example, in a hybrid disk including a first recording layer having the DVD format and a second recording layer having the HD-DVD format, when the focus servo control is performed by irradiating a beam having a wavelength of about 650 nm to read data from the first recording layer, a part of the beam transmitted through the first recording layer, which has a predetermined intensity or more, is reflected from the second recording layer. In this case, an optical pickup device erroneously determines the hybrid disk as a dual layer DVD disk. This may cause a malfunction of the player.
Therefore, in the hybrid disk including recording layers that are different in format from each other, when the data is read from one of the recording layers, the reflectivity and transmissivity of the other recording layers must be properly set so that the intensity of the beams reflected from the other recording layers can be reduced to be lower than a predetermined level.